Rich dropDownMenu using style: rich-menu-list-border

I am trying to get the opened menu of the dropDownMenu component in a state, that the underlaying selectboxes are not in select if I hover the menuitems.

Direct under the dropDownMenu I have a selectBox.
Each time when I hover over my dropDownMenu, the menu is popuped below over the other selectBox. When I hover over the items of my dropDownMenu, the cursor gets the other selectBox selected, not the dropDownMenu.

Is there any possibility to get the visibility or the focus to the dropDownMenu?
I tried with the style rich-menu-list-border.